Create and use our own AppId

[berkus]

(reference here)

Do not hardcode AppId in the code, this part is for CI vaults or something.

[leha-bot]

I created one. We should think now how to integrate it

[leha-bot]

From chat: we should use ENV variables and parse it in CMake instead of curremt CUSTOM_API_ID

[leha-bot]

Task list:

• [x] Create app id;
• [ ] Get rid of strange #include at that place;
• [ ] Create ENV with MTProto tokens in CI;
• [ ] Parse ENV in CMakeLists.txt.

[berkus]

And ENV should be populated from a secure CI vault (travis/2 or appveyor/2)